FIG. 5 illustrates a conventional power miter box with a base 1 and a fence 2 which is mounted on the base 1 for supporting against a workpiece 7. A module member 4 supports a circular blade 5 connected to a hinge 3 which extends from a rear portion of the base 1. An arm member 8, containing a main switch 6, manipulates the blade 5 toward and away from the workpiece 7. An upper guard 10 shields an upper portion of the blade 5 and is mounted on the module member 4. A lower safety guard 11 is connected to a rear portion of the upper guard 10 by a pin 9 and slidingly moves in the inside of the upper guard 10 and shields each side surface of the blade 5.
The blade 5 rotates when the main switch 6 of the arm member 8 is electrically operated by a grasp of a worker's hand. With the activation of the blade 5 the arm member 8 is vertically pivoted downward to make the cut and the bottom edge of the lower safety guard 11 contacts with the upper surface of the workpiece 7 and the lower safety guard 11 moves vertically upward, pivoting around the pin 9 as the arm member 8 is continually operated downward. Thus the blade cuts into the workpiece 7.
However, as the blade is being initially lowered, there exists a possibility of an accident occurring as the blade begins to rotate at high speed while approaching the workpiece. To prevent certain accidents, the above-discussed typical safety device in the power miter box is provided as described in Japanese Utility Model Laid-Open No. 62-128802. However, this safety device focuses on eliminating accessibility to the rotating blade by worker; there is no control of the activation of the operation of the blade which is potentially dangerous, as noted above.